1. Field of the Invention
The present invention generally relates to mixing valves, and more particularly to a thermostatic mixing valve having an improved mixing chamber and a diffuser for facilitating the mixing of a hot fluid and a cold fluid.
2. Discussion of the Related Art
Thermostatic mixing valves are commonly used in plumbing systems. They typically take hot water from a water heater and cold water as supplied to the building by the water company and blend the hot and cold water to a desired intermediate temperature. The blended (or mixed) water is then fed into the hot water supply piping of the building. For a number of reasons it is generally desirable to have the hot water generator produce water hotter than that desired at the plumbing fixture, thus the need for a mixing valve. The valves are so constructed that the temperature of the mixed water remains constant, or nearly constant, regardless of the actual hot and cold water temperatures and regardless of the flow rate.
The prior art valves work fairly well under steady state conditions, i.e., steady pressures and temperatures at all points and parts along the plumbing system. However, when steady state conditions are suddenly disturbed, such as, for example, when a nearby flushometer is being activated, large fluctuations in the mix water temperature can occur. Changes as much as .+-.15.degree. F. have been observed.
A prior art thermostatic valve is shown in FIG. 1. The valve 10 consists of six major components: a body 12, a thermal actuator 14, a spool 16, a biasing spring 18, a body cover 20 and a temperature selection device 22.
The body 12 incorporates a hot port, made up of an external hot port 24a and an internal hot port 24b, a cold port, made up of an external cold port 26a and an internal cold port 26b, and a mix port 28. Body 12 also includes a hot annular groove 56 and a cold annular groove 58. The body 12 and is typically formed from forged or cast metal. The thermal actuator 14 is a device which monitors the temperature of water flowing past it and converts temperature changes into an axial motion via a piston 30. Thermal actuators are made by a number of manufactures, including Vernet. The operating principle of thermal actuators, also called thermal elements, is known in the art and will not be described in detail. Generally, a thermal expansion material (not shown) which is located within cup 32 of thermal actuator 14 expands and contracts in response to increases and decreases, respectively, in the temperature of the fluid which flows past the cup 32. When the thermal expansion material expands, it pushes actuator piston 30 of thermal actuator 14 outwardly. When the thermal expansion material contracts, actuator piston 30 recedes into the thermal actuator 14. A mixing chamber 60 is formed between the bottom of spool 16 and an annular ring 62, which is part of cup 32 of thermal actuator 14.
The spool 16 is located between surface A of the body 12 and surface B of the body cover 20. The distance between surface A of the body 12 and surface B of the body cover 20 is greater than the length l of spool 16. The difference in the distance between surface A of body 12 and surface B of body cover 20 and the spool length l is referred to as the spool stroke, which is the distance that the spool 16 can travel between the surface A of body 12 and surface B of body cover 20. Spool 16 includes an annular cold water chamber 34 and is supported and frictionally engaged within body 12 by O-ring seal 36.
Thermal actuator 14 is threadably coupled to spool 16 within a central hub 44 of spool 16, such that actuator piston 30 is disposed within central hub 44 and such that the actuator piston 30 travels in a direction along the longitudinal axis 46 of the spool 16.
Temperature selection device 22 includes a spindle 40 which is threadably coupled to a handwheel 42. Spindle 40 includes a head 52 disposed within central hub 44 of spool 16 such that it is in direct contact with actuator piston 30. Spindle 40 is frictionally mounted within central hub 44 by an O-ring seal 54. Bias spring 18 is engaged at one end against an internal ridge 50 of body 12 and at the opposite end against annular ring 62 of thermal actuator 14, and biases actuator piston 30 of thermal actuator 14 against head 52 and spool 16 toward surface B of body cover 20. Temperature selection device 22 is operable by turning handwheel 42 in a counterclockwise direction to urge spindle 40 against actuator piston 30, thereby forcing spool 16 away from surface B of body cover 20 and toward surface A of body 12. Conversely, handwheel 42 is turned in a clockwise direction to draw spindle 40 away from actuator piston 30, thereby allowing the bias force provided by bias spring 18 to push spool 16 toward surface B of body cover 20 and away from surface A of body 12. As further described below, this adjustment of the distance between spool 16 and surfaces A and B changes the ratio between the hot and cold water which is being mixed by the valve 10. A typical range is 80.degree. F.-120.degree. F. but almost any range required can be provided.
The operation of valve 10 will now be described. Hot water enters the body 12 through the external hot port 24a, as shown by dashed lines 80, fills the hot annular distribution groove 56, and then flows radially inward through the internal hot port 24b into the mixing chamber 60. Cold water enters the body 12 through the external cold port 26a, as shown by dotted dashed lines 82, fills the cold annular distribution groove 58, flows radially inward through the internal cold port 26b into the annular cold water chamber 34 and then flows through a series of holes located in the spool 16 into the mixing chamber 60. Hot and cold water blend in the mixing chamber 60 to provide water having a temperature somewhere between the hot water and cold water temperatures. This mixed water, shown by solid lines 84, is discharged from valve 10 through mix port 28.
If the temperature of the cold water supply decreases such that the thermal expansion material within cup 32 of thermal actuator expands, actuator piston 30 is pushed outwardly from thermal actuator 14 against head 52 of spindle 40. This causes thermal actuator 14 to pull spool 16 away from surface B of body cover 20 and toward surface A of body 12. As spool 16 is pulled toward surface A, the width of the internal hot port 24b decreases, thereby decreasing the amount of hot water which is allowed to pass into mixing chamber 60. At the same time, as spool 16 is pulled away from surface B, the width of the internal cold port 26b increases, thereby increasing the amount of cold water which is allowed to pass through annular cold water chamber 34 and into mixing chamber 60. The resulting mix of water discharged through mix port 28 therefore has a temperature which is closer to the desired temperature set by the temperature selection device. As the temperature of the mixed water decreases, the thermal expansion material contracts, causing actuator piston 30 to recede into the thermal actuator. Bias spring 18 then forces thermal actuator 14 and spool 16 toward surface B, thereby allowing internal hot port 24b and internal cold port 26b to return to their steady-state positions.
If the temperature of the hot water supply decreases, the opposite action occurs in thermal actuator 14 and, as piston 30 retracts into the thermal actuator 14, spool 16 is pushed toward surface B by bias spring 18. This causes the width of the internal hot port 24b to increase, thereby increasing the amount of hot water which is allowed to pass into mixing chamber 60. At the same time, as spool 16 is pushed toward surface B, the width of the internal cold port 26b decreases, thereby decreasing the amount of cold water which is allowed to pass through annular cold water chamber 34 and into mixing chamber 60. The resulting mix of water discharged through mix port 28 therefore has a temperature which is closer to the desired temperature set by the temperature selection device.
As described above, the amount of actuator piston extension is a function of the temperature of the element. This fact is exploited to provide the temperature control for the mixing valve 10. The spool 16 will settle in at the exact axial position which delivers the mix water temperature that is consistent with the actuator piston 30 extension of that temperature. Should a disturbance occur, such as for example, an increase in the hot water supply temperature, the mix temperature is momentarily also increased. The thermal actuator 14 reacts to this increase of mix temperature with a corresponding increase in the extension of actuator piston 30. Since thermal actuator 14 and spool 16 are biased against each other, the spool 16 is driven downward, thus decreasing the size of the internal hot port 24b while simultaneously increasing the size of the internal cold port 26b, thus restoring the desired mix temperature. As is readily apparent, when the axial position of the adjustment spindle 40 is changed (when turning hand wheel 42, spindle 40 moves up or down in the spindle thread 70) the resulting mix temperature also changes. The total achievable range is determined by the specific characteristics of the thermal actuator 14.
There are several shortcomings of the mixing valve 10 described above. First, the mixing chamber 60 is too small to allow the hot and cold water to thoroughly mix before passing by the cup 32 of the thermal actuator 14. This can cause wide ranges of temperatures which are flowing across thermal actuator 14, which can result in inaccurate reactions of the thermal actuator 14. This causes the actuator to read and respond to a false mix temperature. When, some distance downstream of the valve, the water does become thoroughly mixed, its temperature may be significantly different from that which the thermal actuator 14 sensed.
Another shortcoming is the positioning of the bias spring 18 of the mixing valve 10. When the mixed water flows from the mixing chamber 60 toward the cup 32, it is forced through the coils of the bias spring 18 on its way to mix port 28, as shown by solid lines 84. Since some of the water is directed away from the cup 32 by the coils of the bias spring 18, a less accurate reading of the water temperature may be taken by the thermal actuator.
Furthermore, the flow of water through the coils of bias spring 18 can cause the spring to vibrate, thereby creating a noise which is objectionable.
What is needed then is a thermostatic mixing valve which facilitates the mixing of the cold and hot water before the water passes over the cup of the thermal actuator, thus allowing the thermal actuator to more accurately react to the temperature of the mixture, thus enabling the thermostatic mixing valve to more accurately maintain the temperature of the water output from the mix port of the mixing valve. Furthermore a mixing valve is needed which includes a biasing spring arrangement that prevents the water from being directed away from the thermal actuator and does not vibrate, thus eliminating objectionable noises from the mixing valve during operation.